why does not work the change of alpha value in this simple example=
lazarus / 39-Graphics

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dcelso · 2012-10-05 10:47

.pas
Code: [Select]unit Unit1;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs,
ExtCtrls,
  StdCtrls, LCLIntf, LCLType,IntfGraphics;

type

  { TForm1 }

  TForm1 = class(TForm)
    Image1: TImage;
    Label1: TLabel;
    procedure FormShow(Sender: TObject);
  private
    { private declarations }
  public
    { public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.lfm}

{ TForm1 }

procedure toTransparent(var Bitmap: TBItmap; color: RGBQUAD);
var
  i : integer;
  ppixel : PByte;
begin
// Bitmap.BeginUpdate();
 i:=0;
 ppixel := Bitmap.RawImage.Data;
 while  i <= (Bitmap.Width * Bitmap.Height)  do
 begin
   ppixel[i+3]:=255;
   //  Si es el color pasado por parámetro no se verá
   if (ppixel[i]=color.rgbRed) and (ppixel[i+1]=color.rgbGreen) and
(ppixel[i+2] = color.rgbBlue)  then
   begin
    ppixel[i+3]:=0;
   end;
   Inc(i,4);
 end;
 //Bitmap.EndUpdate();
end;

procedure toTransparentLaz(var Bitmap: TBItmap; color: RGBQUAD);
var
  lazBitmap: TLazIntfImage;
  ImgHandle,ImgMaskHandle: HBitmap;
  k, j :integer;
  ppixel : PRGBAQuad;

begin
 lazBitmap:=TLazIntfImage.Create(0,0);
 lazBitmap.LoadFromBitmap(Bitmap.Handle,Bitmap.MaskHandle);

 for k := 0 to Bitmap.height - 1 do
 begin
   ppixel := lazBitmap.GetDataLineStart(k);
   for j := 0 to Bitmap.width - 1 do
   begin
     ppixel[j].Alpha := 255;
     // Si es negro puro no se verá
     if (ppixel[j].Red=color.rgbRed) and
(ppixel[j].Green=color.rgbGreen) and (ppixel[j].Blue = color.rgbBlue) 
then
     begin
       ppixel[j].Alpha := 0;
     end;
   end;
 end;
end;

procedure TForm1.FormShow(Sender: TObject);
var
  bmp : TBitmap;
  v_rgb : RGBQUAD;
begin
  bmp:= TBitmap.Create;
  bmp.PixelFormat:=pf32bit;
  bmp.SetSize(150,150);
  bmp.Canvas.Brush.Color:= clGreen;
  bmp.Canvas.FillRect(20,20,130,130);
  bmp.Canvas.Brush.Color:= clYellow;
  bmp.Canvas.FillRect(50,50,100,100);
  v_rgb.rgbRed:=0;
  v_rgb.rgbGreen:=255;
  v_rgb.rgbBlue:=255;
  toTransparentlaz(bmp,v_rgb);
  // toTransparent(bmp,v_rgb);  <--- This one alternative does not
work, too.
  Image1.Picture.assign(bmp);

  Label1.Caption:=IntToStr(PIXELFORMAT_BPP[Image1.Picture.Bitmap.Pixel
Format]);
  bmp.Free;
end;

end.

.lfm
Code: [Select]object Form1: TForm1
  Left = 290
  Height = 207
  Top = 168
  Width = 222
  Caption = 'Form1'
  ClientHeight = 207
  ClientWidth = 222
  Color = clRed
  OnShow = FormShow
  LCLVersion = '1.1'
  object Image1: TImage
    Left = 0
    Height = 207
    Top = 0
    Width = 222
    Align = alClient
    Transparent = True
  end
  object Label1: TLabel
    Left = 30
    Height = 15
    Top = 160
    Width = 6
    Caption = '0'
    ParentColor = False
  end
end

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HomePlaneR · 2012-10-10 15:09

Firstly, the order of the color components stored in RawImage.Data is
not RGBA but BGRA.
Secondly, TBitmap.BeginUpdate and TBitmap.EndUpdate must be used in
order to change the bitmap content by accessing to RawImage.Data after
operated with the canvas (you have commented these function calls).
Finally, if all the pixels have alpha=0 then the bitmap will not be
completely transparent (the alpha channel will be ignored in this
case). I mean you should provide different aplha values to have the
correct output.